There is a frequent need for establishing connections with tubular pipes within various technical fields, including tubular pipes intended for transport of gaseous as well as liquid media. Flow communication with a tubular pipe is usually achieved by replacing a short part of the pipe with e.g. a T-coupling, whereby it is possible to establish flow communication with, for example, another pipe. In certain cases, the coupling can be combined with a valve member, whereby the flow communication becomes adjustable. A disadvantage with this type of couplings is, that a part of the main pipe must be replaced with a coupling, e.g. a T-coupling, which means that the pipe can not be used for transport of a gaseous or liquid medium when the connection is made.
In order to overcome the above disadvantage, a type of coupling has been proposed, including two housing members, which by means of screws can be attached embracing a tubular pipe with sealing contact against the outer peripheral surface of the pipe. A piston member, having a cutting edge portion, is arranged in one of said housing members together with an explosive charge, and the charge can be initiated by e.g. a hammer blow directed towards an initiating member protruding from the housing member, whereby the piston member is moved in direction towards the embraced tubular pipe and partly past same, thereby removing a wall portion from the pipe. After completed movement, the piston member extends crosswisely in relation to the length axis of the pipe, having a portion of the outer surface extending into the pipe through the opening taken up by removal of a wall portion. Furthermore, the piston member is arranged with a channel extending crosswisely in relation to its length axis, and by rotating the piston member in relation to the opening taken up in the wall of the tubular pipe, an adjustable flow communication is achieved between the tubular pipe and a second pipe attached to the housing member, which second pipe communicates with the channel in the piston members by means of a channel arranged in the housing member.
However, this type of coupling has also a number of disadvantages, even though it must be regarded as a considerable step forward in relation to previously known techniques. For example, when large opening areas are required to facilitate large flow quantities from the pipe embraced by the coupling, the design is restricted by the fact that only a small wall portion can be removed, if the strength of the pipe should not be endangered. The aforementioned type of coupling is not suitable for large pipe diameters, since only a relatively small flow can be obtained from the relatively large flow capacity in the main pipe. An important disadvantage is also, that the piston member is arranged in a predetermined position in relation to the pipe embraced by the housing members, and that corrosion between the outer peripheral surface of the piston and adjacent cut surfaces in the pipe, which cut surfaces are formed in the previously described cutting operation, results in successively deteriorated sealing properties between the piston member and the cut surfaces, and in an earlier stage, the piston member can also, due to corrosion, be more or less restricted from a rotary movement in relation to the pipe. However, the difficulty to achieve efficient sealing properties between the piston member and adjacent cut surfaces is the major problem, which can cause undesired effects, namely a flow past the piston member to the crosswisely extending channel, which can prevent complete interruption of the flow to the connected pipe.